Method for balancing cells or groups of cells in a battery pack

ABSTRACT

A method for balancing cells or groups of cells connected in parallel and in series for a battery pack by providing a continuously balanced state of charge while in a discharge phase, a charge phase, a quiescent phase, a storage phase, or combinations of these phases.

FIELD

The present embodiments relate to a method for balancing a plurality ofcells or groups of cells connected in series and in parallel to form abattery pack system for use in various applications such as,transportation, communication, oil and mineral exploration,oceanographic research and monitoring, pipeline monitoring andmaintenance, various medical applications, and various portableapplications including military applications.

BACKGROUND

Lithium ion battery technology is becoming the standard for rechargeableenergy storage systems. Lithium ion batteries are able to store up tothree to four times as much electric energy as currently usedrechargeable batteries.

However, current lithium ion battery pack balancing technology has thedisadvantage that it requires complex and costly electronic control andbalancing circuitry that may be inactive for long periods of time.

Currently, balancing the capacities of series connected lithium ioncells in a battery pack system is accomplished using resistors connectedby switches across each cell combined with cell voltage monitoring andcomputer control. The resistors dissipate a relatively small amount ofpower and are activated infrequently. Large battery packs with multiplesources of differential leakage currents cause the battery pack capacityto diminish and not be available for rapid use at all times.

Current battery pack balancing technology is not able to balance groupof cells connected in parallel and then series which have been inactivefor long periods of time.

A need exists for a method for balancing various types of battery packsand cells using continuously active control circuitry regardless of thestate of the battery pack.

The present embodiments address these needs.

BRIEF DESCRIPTION OF THE DRAWINGS

The detailed description will be better understood in conjunction withthe accompanying drawings as follows:

FIG. 1 depicts a battery pack system module usable in a method of theinvention for balancing cells of a battery pack using a reverse voltageprotection diode.

FIG. 2 depicts a battery pack system module usable in a method of theinvention for balancing cells using a bypass diode.

FIG. 3 depicts a pack sensing circuit usable in a method of theinvention.

FIG. 4 depicts a battery pack system usable in an embodiment of a methodof the invention with battery pack modules connected in series.

FIG. 5 depicts battery pack system containing battery pack systemmodules connected both in parallel and in series usable in an embodimentof the invention.

FIG. 6 depicts a sequence of steps for an embodiment of a method used tobalance the battery pack system module depicted in FIG. 1

FIG. 7 depict a sequence of steps for an embodiment of a method used tobalance the battery pack system depicted in FIG. 4.

FIG. 8 depicts a digital controller usable in implementing an embodimentof a method of the invention.

The present embodiments are detailed below with reference to the listedFigures.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Before explaining the embodiments in detail, it is to be understood thatthe embodiments are not limited to the particular description, and thatthey can be practiced or carried out in various ways.

Cell balancing incorporated with protection circuits have only beenavailable for 4 series lithium ion cells. Traditionally, balancing isonly accomplished during charge phase. The embodiments address cellbalancing in any one of four states, which include quiescent, charge,discharge and storage.

The present embodiments are generally related to a method for balancinga plurality of cells connected together in parallel and then the cellsconnected in parallel form groups that can connect in series.

The present embodiments can extend the power duration of battery packsof lithium ion cells to create high energy per ounce battery packs witha longer life in comparison to lead acid or other rechargeablebatteries. Lithium ion cells and lithium ion battery packs are highlydesirable as a source of power because of their high energy capacity,low weight, small size, and potential for long life. The presentembodiments should also work with various types of battery systems.

The present embodiment enables lithium ion battery pack systems to bebalanced at all times or continuously balanced, thereby extending thelife cycle of the lithium ion cells or groups of lithium ion cells. Thepresent embodiments should enable the balancing of other types ofbattery systems. The present embodied method enables minimal loss ofcapacity of the battery pack system while providing a light weight,continuously balanced battery pack.

The present embodiments cause improved power duration for balancedlithium ion cells or groups of lithium ion cells connected in series, orconnected in parallel and in series.

The present embodiments can monitor and measure parameters for aplurality of lithium ion cells connected in parallel or groups oflithium ion cells connected in parallel and in series. The presentembodiments can be used to determine the relative state of charge forindividual lithium ion cells connected in parallel or for groups oflithium ion cells connected in parallel and in series.

The present embodiments provide a method to balance battery pack systemsat all times, continuously. The method can be used when the batterycells are in a discharge phase, a charge phase, a quiescent phase,storage, or combinations of these conditions.

After measuring and monitoring, the method can remove portions of astate of charge for at least one of the individual cells connected inparallel or at least one of the groups of cells connected in parallelthen in series, if the cell or groups of cells exceed a preset limit.

With reference to the figures, the method can be understood with regardto the apparatus and software usable to implement the exemplaryembodiments of the method.

FIG. 1 depicts a battery pack control module 6 with protective circuitrythat includes a reverse voltage protection diode 28. The reverse voltageprotection diode 28 connects to a disconnect circuit 12, as well as agroup of cells connected in parallel 20 in the implementation of anembodiment of the method.

The battery pack control module 6 includes a controller assembly 8connected to the disconnect circuit 12. The controller assembly 8 canexecute instructions to engage or disengage the disconnect circuit 12.The controller assembly 8 can communicate with the voltage regulator 42,a monitor or initializer 50, a balancing circuit 25 a and 25 b, and apack sensing circuit 21.

In the method, monitoring and measuring of cell voltage, temperature,and current is performed. To implement the method, FIG. 1 shows anexemplary device for measuring cell voltage 24 usable within thecontroller assembly 8. The controller assembly 8 can connect to theseries connected groups of cells connected in parallel 19 and 20.

If a device for measuring cell voltage 24 is used in the method, but thedevice is connected outside of the controller assembly 8, then the packsensing circuit 21 can connect directly to the series connected groupsof cells connected in parallel 19 and 20, and the controller assembly 8does not have to connect directly to the series connected groups ofcells connected in parallel 19 and 20.

The method contemplates a step for preventing excessive voltage fromcrossing the controller assembly. To implement this method, FIG. 1depicts a reverse voltage protection diode 28 for preventing excessivevoltage from developing across the controller assembly 8, the voltageregulator 42, and the disconnect circuit 12.

The method contemplates that the controller assembly 8 can include ananalog controller 9 and a digital controller 10 to implement computerinstructions 44 when temperature, voltage, and current exceed presetlimits which are obtained from a configuration table with statisticsthat are saved in memory of a processor of the digital controller 10 inoptional data storage, not shown in FIG. 1.

Exemplary analog controllers usable with the method are those availablefrom Texas Instruments of Dallas, Tex., Part Number BQ29312A.

An exemplary digital controller 10 can be circuitry that includes one ormore analog I/O ports, one or more digital I/O ports, a processor, whichcould be a microprocessor, memory which can be a flash memory andprocessing logic located in the memory, as well as additional computerinstructions in the memory for directing the processor to performdischarge of current functions when one or more measured values fortemperature, current or voltage exceed or drop below a preset limit froma configuration table.

The method contemplates that the digital controller can include at leastone configuration table. The configuration table can be a table, groupsof tables, or can be programmable data about the cells to be balanced.Additional data storage can be used in communication with the processorfor storing the configuration table, as well as storing computerinstructions for operating the circuitry of the balancing circuit andfor storing additional data related to the configuration table. The datastorage can include the monitored and measured data obtained by thebattery pack control module, such as cell voltage, current and/ortemperature. The monitored and measured data of the method can berecorded and stored in database format or a table format.

The method contemplates the use of a disconnect circuit 12 with a chargeswitch 13 and a discharge switch 14 which can be connected in series.

The charge switch 13 can be a transistor switch such as a Vishay P-FETswitch of Malvern, Pa. The discharge switch can be the same part as thecharge switch or a similar type of switch.

A lithium ion cell 15 can be connected in parallel to a lithium ion cell16. A lithium ion cell 17 can be connected in parallel to a lithium ioncell 18. A plurality of lithium ion cells 19 connected in parallel canbe connected in series to a plurality of lithium ion cells connected inparallel 20. A group of parallel-connected lithium ion cells can beconnected as groups in series 200.

The method contemplates using balancing circuits 25 a and 25 b eachhaving a shunt resistor, depicted as elements 26 a and 26 brespectively, and each having a bypass switch depicted as elements 27 aand 27 b respectively to facilitate the balancing step after monitoringand measuring and then comparing is completed.

In a preferred embodiment, the method contemplates using a shuntresistor across groups of cells connected in series through the bypassswitch.

The method contemplates using a pack sensing circuit 21 that connects tothe controller assembly 8 and the groups of cells connected in series 19and 20. The pack sensing circuit 21 can include various sensors,measuring means and monitoring means. The pack sensing circuit 21 can beused to measure any combination of cell voltages in groups of cells inseries. The pack sensing circuit 21 can also be used to measuretemperatures of a cell, temperatures of groups of cells, or temperaturesbetween groups of cells. The pack sensing circuit 21 also has a devicefor measuring cell voltages 24 between cells, between groups of cells orcombinations thereof. One or more current measuring, cell voltagemeasuring and/or temperature measuring devices can be used in theembodied method.

An embodiment of the method contemplates that the device for measuringcell voltages 24 between cells, between groups of cells or combinationsthereof, can be internal to the analog controller 9. The means formeasuring cell voltages can be within the analog portion of thecontroller assembly 8. An example of a device usable for measuring cellvoltages could be a Texas Instrument analog controller that additionallymeasures voltage, which is available from Texas Instruments of Dallas,Tex.

The pack sensing circuit 21 can include a device for measuring batterypack temperature 22, which can be external to the controller assembly 8.This temperature sensing device can be any thermistor such as those fromCTS of Elkhart, Ind.

Additionally, an embodiment of the method contemplates that the packsensing circuit 21 of FIG. 1 can include a device for measuring batterypack current 23, which can be external to the controller assembly 8. Thedevice for measuring battery pack current can be a resistor, such asthose available from Vishay of Malvern, Pa.

The method contemplates using balancing circuits 25 a and 25 b that caninclude shunt resistors 26 a and 26 b connected to by-pass switches 27 aand 27 b. The by-pass switch 27 a or 27 b can be a semiconductor switch,a variable resistor, a mini-micro switch or combinations of thesedevices. The balancing circuits 25 a and 26 b can be used to connectbetween the plurality of cells 15, 16, 17, 18 or between the groups ofparallel connected cells 19 and 20 which can be connected in series 200.The controller assembly 8 can activate balancing activity by engaging orcontrolling the balancing circuits 25 a and 25 b.

The present embodiments can include computer instructions 44 that can beused with the controller assembly 8 to direct the controller assembly 8to activate disconnect circuit 12 to disconnect cells from a load 46 ora charger 48 and thereby enhancing the balancing of the groups in series200, and for battery pack system module 202 safety.

The computer instructions 44 can be stored in the memory of a processorof a computer or server usable in the embodiments, which can includeinstructions to initialize and control the analog controller 9 forbattery pack system module 202 safety and to enable or disableindividual balancing circuits 25 a and 25 b at anytime, to keep groupsof cells in series 200 continuously in balance.

In addition, the method contemplates using a battery pack control module6 with a voltage regulator 42 for powering the controller assembly 8.The voltage regulator 42 can be a DC programmable voltage regulator suchas those made by Linear Technology, Inc. of Malpitas, Calif.

The embodied method contemplates that a monitor or initializer 50 can beconnected to the controller assembly 8, such as the type made by HewlettPackard of Palo Alto, Calif.

A load 46, which is also referred to herein as an application, can beconnected to a battery pack system module 202. A charger 48 can beconnected to the battery pack system module 202. In FIG. 1, a line isdepicted around battery pack control module 6 with the plurality ofcells connected in parallel, further connected in series 200, which ishereafter termed “a battery pack system module 202.”

FIG. 2 depicts an alternative embodiment to that shown in FIG. 1. InFIG. 2, a bypass diode 29 can be utilized instead of a reverse voltageprotection diode 28. Bypass diodes are available from ON Semiconductorof Phoenix, Ariz., and Vichay of Malvern, Pa.

FIG. 3 provides a detailed view of the pack sensing circuit 21 usable inthe embodied method. The pack sensing circuit 21 of FIG. 3 can include adevice for measuring battery pack temperature 22, a device for measuringbattery pack current 23, and a device for measuring cell voltages 24, orcombinations thereof.

FIG. 4 depicts a detailed view of a battery pack system 40 which can beoperated by the embodied method. The battery pack system 40 depicts aplurality of at least two battery pack system modules shown connected inseries as elements 202 a and 202 b to form a battery pack system 40. Thebattery pack system modules 202 a and 202 b typically have the samenumber of groups of cells connected in parallel but need not contain thesame number of these parallel groups connected in series. The pluralityof cells or groups of cells are lithium ion cells, such as those soldthrough Southwest Electronic Energy Corporation of Houston, Tex.

FIG. 4 shows an application 46 connected to the battery pack system 40and a charger 48 also connected to the battery pack system 40.

A discharge resistor 52 is depicted connected to the battery pack system40. Discharge resistors are available from Vishay of Malvern, Pa.

The embodiments contemplate balancing the state of charge of at leasttwo battery pack system modules connected in series 202 a and 202 b bydischarging the battery pack system 40 using a discharge resistor 52until a balanced state is achieved. The bypass diode 29 shown in FIG. 2that is contained within each battery pack system modules 202 a, 202 bfacilitate the balancing of these two series connected battery packsystem modules.

The battery pack system modules 202 a and 202 b are contemplated to beavailable for use anytime, even if the battery pack system 40 has beenin an idle state, a discharge state, a quiescence state or in storage,which can be long term storage. The battery pack system modules 202 aand 202 b can be individually available for use at full capacity anytime due to the internal balancing circuit shown in FIG. 1 and FIG. 2.Alternatively, if the battery pack system 40 contains battery packsystem modules 202 a and 202 b that are not balanced, the battery packsystem 40 will require the discharge balancing described above beforethe battery pack system 40 is available at full capacity.

FIG. 5 depicts a plurality of battery pack systems containing at leasttwo battery pack system modules that are connected both in parallel andin series 202 a, 202 b, 202 c, and 202 d.

FIG. 6 depicts a sequence of steps used to balance the battery packsystem module of FIG. 1.

The method involves monitoring and measuring parameters for a pluralityof cells or groups of cells connected in parallel and in series todetermine a state of charge for individual cells 100.

The method of step 100 can include the step of monitoring and measuringthe temperature of lithium ion cells or groups of lithium ion cells 102,the step of monitoring and measuring the current of the lithium ioncells or groups of lithium ion cells 104, and the step of monitoring andmeasuring cell voltages for lithium ion cells or groups of lithium ioncells 106.

The monitoring and measuring is performed using a sensing circuit. Thecircuit includes thermistors, comparitors, resistors, voltagetranslators and similar components for sensing temperature, voltage andcurrent. The measured data is stored in the digital controllerpreviously noted in FIG. 1.

The next steps involve using data from a configuration table tocustomize the balancing system for the cells or groups of cells to whichthe balancing system is connected, the groups of cells, shown in FIG. 1.The step for using the data is indicated as step 108.

An example of the step of using a configuration table can be using adatabase stored in data storage connected to a processor or using adatabase stored in memory of a processor which contains thespecifications of the cells or groups of cells connected to the batterypack system module. An example of the specifications usable in theconfiguration table would be Sanyo specifications which describe aparticular group of Sanyo cells used in the groups of cells in series.

The specifications can include data such as the capacity ranges of thecells, the temperature limits of the cells, or the range of currents ofthe cells or another limit of the cell, such as voltages ranges that thecell can be charged between or discharged between. Other data that canbe included in the configuration table can be specifications on the loador application to which the battery pack is to be applied, one or moremethods for charging the battery pack, the environment for battery packoperation, and maximum application limits.

The method can be used to control excessive current across the cells.The method can be used to make sure the voltage across the cells iswithin optimum ranges, therefore not excessively high or low. The methodcan be used to control excessive temperatures across the cells connectedin series, insuring that the temperatures are not too high or too low.The method contemplates that the pack can be opened if the temperatureis too high,

Additionally, the method contemplates steps which provide data to a userinterface, such as a graphics user interface (GUI) which indicates thatthe temperature across the cells or groups of cells is too high andpermits user intervention. This step is depicted as element 110. If aGUI is used, the GUI can display multiple parameters, such astemperature, voltage, current, and computed data (for example, capacity,time to empty, time to full, balance status, and the like). Theseexample parameters can be captured or calculated at a future time andmost are Smart Battery (SMB) parameters.

Element 112 is the step of balancing the state of charge of groups ofcells in series by discharging the groups of cells in series orplurality of cells of cells in parallel until a balanced state isachieved. As shown in FIG. 1, a balancing circuit 25 is used with ashunt resistor and a bypass switch to facilitate the balancing.

The method can be used to achieve a balanced state of charge for theplurality of cells or groups of cells while in a discharge phase, acharge phase, a quiescent phase, and in storage.

FIG. 7 depicts another sequence of steps used to balance a battery packsystem.

In FIG. 7, the first step is to use a discharge resistor to disconnect agroup of battery pack modules to discharge the series connected batterypack system modules until they all disconnect 300.

The method contemplates a sequence of steps wherein the battery packmodules are maintained in a protect stage. Each of the battery packmodules opens up by opening a discharge switch in each of the batterypack system modules 302. The discharge switch can be used until a presetlimit is achieved by all of the battery pack modules 304.

The preset limit can be ascertained by comparing true voltages to valuesin the configuration table 306, which are the values for achieving abalanced state. The bypass diode shown in FIG. 2 can be used to carrythe current of the battery pack modules that have been disconnected 308.

FIG. 8 shows an embodiment of a digital controller 10, which can includeone or more analog I/O ports 30, one or more digital I/O ports 42, aprocessor 32, and memory 34 with processing logic 36, and computerinstructions 44 within data storage 38, or alternatively within memory34 for directing the processor 32. The digital controller 10 can includeat least one configuration table that optionally, can be a programmabletable, adapted for storage in memory or data storage. Data storage 38can be in communication with the processor 32 for storing the computerinstructions 44.

The digital controller can be used to execute computer instructionswhich can monitor and measure the state of charge for the plurality oflithium ion cells or groups of lithium ion cells; monitor and measurecurrent through the plurality of lithium ion cells, monitor and measuretemperature of the plurality of lithium ion cells, monitor, initialize,and activate the analog controller, activate at least one disconnectcircuit for safety between the plurality of lithium ion cells or groupsof lithium ion cells; and activate at least one balancing circuit toachieve balance between the plurality of lithium ion cells or groups oflithium ion cells.

The digital controller is used to execute computer instructions formonitoring the state of charge of the lithium ion cells or groups ofcells and removing at least a portion of the charge to achieve balancebetween the plurality of cells or group of cells.

The method can include the step 206 of using the digital controller toexecute computer instructions for monitoring the state of charge of thelithium cells or groups of cells and removing at least a portion of thecharge to achieve balance between the plurality of cells or groups ofcells.

While these embodiments have been described with emphasis on theembodiments, it can be understood that within the scope of the appendedclaims, the embodiments might be practiced other than as specificallydescribed herein.

1. A method for balancing a battery pack having a plurality ofindividual cells or groups of individual cells connected in series, orconnected in parallel and then in series, the method comprising thesteps of: a. monitoring and measuring parameters for a plurality ofindividual cells connected in parallel or groups of individual cellsconnected in parallel and then some of the plurality or groups areconnected in series, to determine a state of charge for the individualcells connected in parallel or the individual groups of cells connectedin parallel and then in series wherein the monitoring and measuring stepfurther comprises measuring a temperature of the cells or the groups ofcells; measuring current of the cells or the groups of cells; andmeasuring cell voltages of the cells or the groups of cells, and b.removing at least a portion of a charge from the plurality of individualcells connected in parallel or groups of individual cells connected inparallel and then in series to achieve a balanced state of charge forthe plurality of individual cells or groups of individual cells while ina discharge phase, a charge phase, a quiescent phase, and a storagephase, further comprising using a digital controller to execute computerinstructions to balance the cells, wherein the computer instructionsinstruct a processor connected to the plurality of cells or groups ofcells to execute the steps comprising: monitoring and measuring thestate of charge for the plurality of cells or groups of cells;activating at least one disconnect circuit between the plurality ofcells or groups of cells; when the monitoring and measuring valuesextend beyond preset limits; and activating at least one balancingcircuit to manage the removal of at least a portion of a charge from theplurality of cells or groups of cells to achieve balance.
 2. The methodof claim 1, further comprising the step of using a configuration tableto customize the balancing of the state of charge for the individualcells or groups of individual cells, or combinations thereof.
 3. Themethod of claim 1, further comprising the step of connecting theplurality or individual cells or groups of individual cells together inseries to form at least one battery pack system.
 4. The method of claim1, further comprising the step of preventing excessive voltage fromdeveloping across the individual cell or groups of individual cells. 5.The method of claim 1, wherein the step of removing a portion of thecharge For at least one individual cell or at least one group ofindividual cells until the balance state uses a disconnect circuit and adiode.